Phonograph pickup device



Patented July 8, 1947 UNITED STATES PATENT OFFICE PHONOGRAPH PICKUP DEVICE vania Application September 8, 1944, Serial No. 553,156

1 Claim.

The present invention relates to a phonograph pick-up for utilization with frequency modulation radio receivers and particularly to a pick-up of the inductance type which has high sensitivity as compared with other pick-ups of the same general type.

It is an object of this invention to provide a device which will effect the foregoing by aiding rather than diminishing the flux lines and by concentrating these flux lines into narrower paths.

Further objects and features of my invention will be apparent when the following description is considered in connection with the annexed drawing in which:

Figure 1 is a longitudinal, vertical, cross-sectional view of the device of my invention; and

Figure 2 is a cross sectional View of the device taken upon the line 22 of Figure 1.

Both figures are on an enlarged scale.

Referring now to the drawing it will be seen that the device comprises a housing 10 formed of non-magnetic material, this housing being illustrated as being generally square in cross section although, of course, any other form desired may be utilized. Within the housing Ill there are two iron shells l l and I2 which are made of high permeability powdered iron and comprise cuplike members having the upstanding pole pieces I3 and M at their centers. In the annular spaces formed between the exterior walls and the pole pieces II and I2 are two coils l5 and I6 which may be wound upon the spools l1 and i8 and thereafter slipped into place in the annular spaces mentioned or if desirable may be placed in the annular spaces without use of the spools.

A disk 20 of high permeability powdered iron and of substantially the same cross sectional dimension as the pole pieces l3 and I4 is located in the gap between the pole pieces, this disk being supported on the upper end of the lever 2|, which lever is mounted, as, for example, by means of the pin 22, for movement across the pole pieces. Pin 22, as clearly indicated in Figure 1, is supported in the housing Ill and the lower end of lever 2| extends through a slot cut in the housing and terminates in a stylus 23 which is designed to cooperate with the grooves of the ordinary phonograph record.

Lever 2| is mounted rigidly on pin 22 so that disk is normally positioned with its center separated from the axis of the pole pieces [3 and M, as shown in Figure 2. A torsional resilient force tending to hold lever 12] in this position is provided" by pin 22, or by any other convenient spring means.

It will be seen that as the stylus moves in the grooves of the phonograph record the disk 20 moves to positions such that its axis is more or less nearly coincident with the axis of the pole pieces l3 and M. By this means the reluctance of the magnetic circuit is changed and the magnetic flux about coils l5 and I6 is increased and. decreased and the frequency of the associated resonant system correspondingly decreased and increased.

It will also be clear that the use of the high permeability iron disk tends to raise the overall Q of the resonant circuit of which the coil forms a part. It will also be seen that the introduction of the iron of disk 20 makes the lines of magnetic flux follow along the pole pieces and therefore requires a much smaller movement of the lever 2i and stylus 23 in order to produce a given change in the resonant frequency of the resonant circuit comprising the coil and its associated shunt condenser (not shown). A suitable oscillator circuit for use with the frequency modulation pick-up of the present invention is described in United States Patent No. 2,322,621, issued June 22, 1943.

While I have described a preferred embodiment of my invention it will be obvious that other embodiments and constructions may be adopted without departing from the spirit thereof and, consequently, I desire to be limited not by the foregoing description. but solely by the scope of the appended claim.

What is claimed is:

In a phonograph pick-up ior modulating the frequency of an oscillator, in combination, a pair of cylindrical members of high permeability material, each of said members having an annular depression therein to form an outer shell and an inner pole piece, said pole pieces being shorter than said shells, coils in said annular depressions, means mounting said cylindrical members with the rims of the shells in abutting relationship forming a space between said pole pieces, a disk of high permeability material mounted in said space between said pole pieces, and a lever carrying said disk, said lever terminating in a stylus at its 013-- posite end whereby movement of said stylus in accordance with the grooves of a phonograph record or the like will move said high permeability disk into and out of a normal position in which its axis is more or less nearly coincidental with the axis of said pole pieces.

BRUCE ROBERTS.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Andrewes Oct. 22, 1929 Meissner May 18, 1943 FOREIGN PATENTS Country Date France 1930 Germany 1914 Australia 1943 

